compression values

[tbernd]

Hi,

yesterday I measured compression. I got this values:

Cylinder 1 to 6 = 180 psi
Cylinder 7 = 150 psi
Cylinder 8 = 170 psi

Any comments?


Cheers

Bernd

[Jack Valiant]

What's the mileage on the engine? If she has a decent amount of mileage then I would not be too bothered in this slight variation. Keep a record and recheck at service time fella.

[keatsie]

Was the engine hot or cold?

[Number 7]

It should be tested hot with wide open throttle. There's a very good article about this on Dave Bakers website which I'll post a link to tonight. From memory, a good engine should give a max of about 20 times the static cr. I've tested mine a couple of times , once quite recently, so will compare your values.
Edited for crap spelling on a Iphone

Edited by Number 7 on Thursday 24th October 20:30

[tbernd]

Hi mates,

engine was warm, throttle full open.Milleage is about 55000 miles.

Cheers Bernd

[adam quantrill]

If you want a bit more detail then put a teaspoon (2.5ml max) of engine oil down the spark plug hole and re-run the test.

This will seal up (temporarily) most ring problems. It may splatter up and coat the valves. It may improve a badly-seating valve but not help if there's a chip.

So if the reading recovers then it'll tell you a bit about it.

But I agree it'll still run reasonably well.

Edited by adam quantrill on Thursday 24th October 20:10

[Number 7]

See this guide, written by Dave Baker who posts here on PH.

http://www.max-boost.co.uk/max-boost/internet_arti...

Lots of variables, but if you have the standard 9.75:1 CR, you should expect to see 165 - 195 psi, with no more than 10% variation across all cylinders. Your figures look ok, except that the lowest is 16% less than the highest. Not dramatically bad, but I would re-test, and if there is still a similar variation, do as Adam suggests, and perform a wet test, which should give some clue to any potential problem. If you have the original cam, it could be that it is beginning to show signs of wear, which would not be untypical at that type of mileage. I wouldn't be overly worried at this stage though.

[mrzigazaga]

Mmmm…Could be a stab in the dark but like what has been said about cam wear my 280i had similar compression figures..In fact they were not that far from what you have..I too had a 15-20% variable and the following year after a round trip of about 500 miles..Some of them being 100mph on a private runway..My cam wore enough to recess a valve almost beyond adjustment..But then i did have leaded heads…However once the hard stuff wears from a cam the metal underneath is comparably soft and its only a matter of time..Ziga